What prevented civilizations before Rome from conquering Greece?

The Greeks themselves did. The Greek Phalanx was the most sophisticated military structure of the Age, and was virtually invincible, even when vastly outnumbered by less organized military forces. Also, Greek naval power was second to none, since the Greeks were a nation of merchants and pirates, to a large degree. Furthermore, the Greek territories weren’t particularly rich, they didn’t have much arable land, for example. There was no reason for empires to take much trouble to bother the Greeks in their native territories. And, if they did, as the Persians tried to, they lived to regret their error! https://www.quora.com/unanswered/What-prevented-civilizations-before-Rome-from-conquering-Greece